Such closure elements are used in engine housings and in hydraulic and pneumatic systems that work with relatively low pressure. In automotive construction these are inserted tightly into bores of engine housings, for example. Closure elements of this type can be produced inexpensively and in addition are easy to fit and remove.
A closure element of this type is disclosed in EP PS 0 364 699 B1. Here the closure element is in the form of a solid sphere that can be pressed into a plug recessed into the bore. The solid sphere works here as an expansion element for the plug. However, it can also be pressed directly into the bore that is to be closed. In both cases the diameter of the sphere is oversized in comparison to the bore so that perfect tightness of the closure is guaranteed. If the solid sphere is pressed directly into the bore that is to be closed, a high radial pressure is generated on the circular pressing surface upon pressing in, and this may cause damage to the bore.